Prepare stuffing mix with water; set aside. In a bowl, combine cooked diced chicken, thawed broccoli, and undiluted broccoli-cheese soup. Spread in greased 11?7 baking dish. Top with prepared stuffing, then sprinkle cheddar on top. Bake covered ~20 minutes at 350?F, then uncover and bake 10?15 minutes more until heated through and cheese is melted..